One-hundred and eighty-seven general practitioners in western Norway recorded smoking habits among 2379 women, consulting for their first regular medical check-up in pregnancy. Forty-six per cent had been daily smokers the last 3 months before pregnancy. Thirty-nine per cent were still smoking at the time of their first check-up. Sixteen per cent of the daily smokers stopped smoking spontaneously during the first few weeks of pregnancy. Fifty-seven per cent of women younger than 20 and 28% of women 30 years and older, did smoke at the first check-up. Single women smoked more often than women living with a partner (58% versus 38%). Smoking habits were not associated with number of previous pregnancies. At the first check-up, 530 pregnant women, still smoking daily, 18-34 years of age, living with a partner, accepted to participate in a smoking intervention study. They filled in a questionnaire about their smoking habits, the smoking habits of their partners and their attitudes towards smoking cessation. Sixty-five per cent reported a reduction in their use of cigarettes after becoming pregnant. The mean reduction in the number of cigarettes smoked daily was 4.0 (31%). Most of the respondents expressed a strong motivation to quit or reduce their smoking habits during their pregnancy. Seventy-two per cent of the partners were daily smokers. Reduction in the consumption of cigarettes, negative attitudes towards smoking and determination to stop smoking was significantly higher among women who were encouraged by their partners to stop smoking and in those who perceived that their partners were willing to reduce their consumption.